1. Field of the Invention
The present invention relates to a capacitor, a circuit board with a built-in capacitor wherein a capacitor is incorporated in the interior of the circuit board, and a method for producing such a capacitor and a circuit board with a built-in capacitor.
2. Description of the Related Art
As is well known, there are semiconductor packages which require built-in capacitor components. To satisfy this requirement, a capacitor component is generally mounted as a chip onto an uppermost layer of the semiconductor package or to incorporate the capacitor element in a printed circuit board. For example, Japanese Unexamined Patent Publication (Kokai) No. 6-252528 discloses a printed board carrying thereon a film-like capacitor element as shown in FIG. 1. A printed board 101 has a wiring layer 102 of copper (Cu), a metallic layer (a lower electrode) 104 of gold (Au) which is difficult to anodize, a metal oxide dielectric film 106 formed upon anodization of aluminum which is a metal capable of being easily anodized, and a metallic layer (an upper electrode) 107 formed of Au which is the same as the lower electrode or Cu sequentially formed thereon. The respective layer or film can be formed at a predetermined thickness, for example, by a conventional film-forming method, such as plating, vacuum deposition, sputtering or chemical vapor deposition (CVD). In such a laminated structure, an aluminum type film capacitor element is formed from Au film (a lower electrode) 104, Al2O5 film (a dielectric film) 106 and Au film (an upper electrode) 107. Note that if Ta is used in place of Al, a Ta type film capacitor element can be obtained.
Many problems, however, are still unsolved in the prior art capacitor components, including in the film capacitor element described above with reference to FIG. 1. For instance, when the capacitor component is mounted onto the semiconductor package, as a surface area in the outermost layer of the package is restricted, there is a limit in the number of parts which can be mounted. Also, since a distance from a semiconductor chip to the capacitor component (a wiring distance) is increased, a size of the semiconductor package, which must essentially be small, becomes large. In addition, in such a semiconductor package, due to the rerouted wiring of a circuit, a capacitance (electrostatic capacity) increases to disturb a high speed response. Recently, as the miniaturization and the high density integration of the semiconductor package has become more important, the above problems are now serious,
In the conventionally applied element structures wherein the upper electrode is formed directly on the dielectric film formed on the lower electrode, there is a problem that an electrostatic capacity in the resultant capacitor component becomes lower which in turn increases a leakage current. While a thickness of the dielectric film could be increased to reduce the leakage current, such a countermeasure cannot solve the problem of reduction in the electrostatic capacity and also it causes reduction in the yield of the production.
The present invention is directed to solve the above-mentioned problems in the prior art.
One object of the present invention is to provide a capacitor component capable of being mounted onto a semiconductor package without restricting the number of the mounted capacitor components and capable of reducing a distance between a semiconductor chip and the capacitor component so that the miniaturization and the high density integration of the semiconductor package are largely facilitated.
Another object of the present invention is to provide a high performance capacitor component showing a larger electrostatic capacity, higher pressure resistance and less leakage current.
A further object of the present invention is to provide a capacitor component having a high reliability and good production yield.
A further object of the present invention is to provide a small-sized and high-performance circuit board, having the capacitor component, in accordance with the present invention, incorporated therein.
A further object of the present invention is to provide a method of producing the capacitor component and the circuit board with a built-in capacitor according to the present invention in a simple manner and at a high yield.
The above-mentioned objects and other objects of the present invention will be more easily understood from the following detailed description regarding to the preferred embodiments and examples of the present invention.
In one aspect, the present invention resides in a capacitor used while being incorporated in an interior of a circuit board between lower and upper wiring layers, comprising a lower metallic layer formed of at least one valve metal, i.e., valve-acting metal, selected from the group consisting of aluminum, tantalum, niobium, tungsten, vanadium, bismuth, titanium, zirconium and hafnium, a dielectric layer formed of an oxide of the valve metal which may be the same as or different from that of the lower metallic layer, an intermediate layer formed of a solid electrolyte, and an upper metallic layer formed of an electrode metal, layers in the capacitor being laminated in this order.
In another aspect thereof, the present invention resides in a circuit board with a built-in capacitor wherein the capacitor according to the present invention is incorporated in an interior of the circuit board between lower and upper electrode layers.
In a further aspect thereof, the present invention resides in a method of producing a capacitor used while being incorporated in an interior of a circuit board between lower and upper wiring layers, comprising the steps of, after forming the lower wiring layer:
forming on the lower wiring layer a lower metallic layer from at least one valve metal selected from the group consisting of aluminum, tantalum, niobium, tungsten, vanadium, bismuth, titanium, zirconium and hafnium;
forming on the lower metallic layer a dielectric layer from an oxide of the valve metal which may be the same as or different from that of the lower metallic layer;
forming on the dielectric layer an intermediate layer from a solid electrolyte selected from the group consisting of a conductive polymer, organic semiconductor material and conductive metal oxide; and
forming on the intermediate layer an upper metallic layer from an electrode metal.
In a still further aspect thereof, the present invention resides in a method of producing a circuit board with a built-in capacitor wherein a capacitor is incorporated in an interior of the circuit board between lower and upper layers, comprising the steps of:
after forming on a core substrate the lower wiring layer from a conductive metal, forming on the lower wiring layer a lower metallic layer from at least one valve metal selected from the group consisting of aluminum, tantalum, niobium, tungsten, vanadium, bismuth, titanium, zirconium and hafnium;
forming on the lower metallic layer a dielectric layer from an oxide of the valve metal which may be the same as or different from that of the lower metallic layer;
forming on the dielectric layer an intermediate layer from a solid electrolyte selected from the group consisting of a conductive polymer, organic semiconductor material and conductive metallic oxide;
forming on the intermediate layer an upper metallic layer from an electrode metal and, further
forming the upper wiring lower from a conductive metal on the capacitor thus formed.
In this producing method, after forming the first capacitor on the core substrate, an insulation film covering the first capacitor and then a second capacitor on the insulation film may be formed in the same manner as forming the first capacitor. Similarly, a third, a fourth, etc. capacitors may be formed in the same manner,